problems with Adcom GFP-1 preamp & GFA-1A power amp

keymap

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Aug 25, 2013
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I have a 30+ year old system with an Adcom GFP-1 preamp and GFA-1A power amp that worked great and sounded great until a recent move. I moved the components extremely carefully and reproduced the exact same connections precisely and would be very surprised if something was damaged in the move but can't rule that out. But wanted to check here to see if anyone has any suggestions; hoping maybe there is something obvious I have missed as I am not too familiar with these components (inherited them from my dad). The problem is that, as far as I can tell, the power amp is not doing it's job. When I have a source playing out of the stereo, I can't hear a thing unless I turn the volume way up almost to the highest setting and even then it's still quite low. I have done some tests and determined that the speakers are working fine when connected to another (integrated) amplifier, so the problem is not the speakers. Also, if I put headphones in the GFP-1 I can hear perfect audio at normal volumes. The GFA-1A power amp light goes on and fan works fine at normal or high speed; the unit gives no indication of a problem. If I turn off the power amp, I hear no sound out of the speakers at all even at high volume, but with the power amp on I hear the aforementioned extremely low signal. Any ideas what could cause this? Is the problem definitely in the power amp or is it possible the preamp has an issue? Thanks for any advice.

One more note, for testing I don't have any other preamps or power amps, only integrated amps, so it's been hard for me to narrow down the cause of the problem beyond those 2 components. Just for kicks I tried connecting the GFP-1 output into an integrated amp's aux input. The signal in this situation was also very low, volume had to be turned up to max just to barely hear it. Is this the expected outcome or an indication of a problem in the preamp?
 

makkem

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Hi
Since you got low output when plugging the preamp into the aux input this strongly suggests a problem with the preamp or with whatever is plugged into the preamp.

 

keymap

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Aug 25, 2013
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Ok thanks. I tried multiple confirmed working audio sources into multiple inputs of the preamp and had the same issue all around. So it's not the sources. Any idea what exactly this means is wrong with the preamp? Think I should just replace the preamp or is there anything you can think of to suggest I can try to do? I'm starting to wonder if power source could be an issue but just grasping to figure out if there is anything external to the preamp that could still be causing the issue. Or are these units known to be so fragile that extra-carefully bringing it up and down a flight of stairs and on a 5 minute car ride could cause this?
 

keymap

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Aug 25, 2013
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Oh and also I should mention, the GFP-1 has 2 sets of output jacks, and I tried going out through each of them and had the same issue regardless of which output was going into the power amp.
 

makkem

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It would be unusual for a unit of that quality to fail due to that small amount of handling,however it is quite old and capacitors do get less reliable with age especially power supply electrolytics and these problems could be due to the power supply.
I would open it up and check the capacitors and transformer for discoloration and also remove and check any fuses (a fuse not making a good contact can reduce the supply voltage and fuses can vibrate loose)
If it has a mains power plug remove it and make sure the contacts are clean on plug and socket.
 

keymap

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Aug 25, 2013
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Ok good advice - will do and report back. One more question - does the fact that audio plays perfectly fine through the headphone jack of the preamp tell us anything of note? Or not really since the amount of power necessary to drive a headphone jack is miniscule? Sorry for my ignorance on this if that's a stupid question.
 

makkem

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The headphones are driven by an integrated headphone amp which may handle reduced power better.
It may be worth investigating the power amp ,does it have a volume control,if so try plugging your cd player directly into the power amp as this will be at line level the same as your preamp.You should start with the volume low then increase.Do not do this if the power amp has no volume control as you will get full power to your speakers.
 

keymap

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Aug 25, 2013
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Ok problem identified - it's the power amp rca input jacks. I noticed after unplugging the jacks leading to the preamp that the input jacks were really loose. When I opened up the case to see what was going on under there, it was apparent that the jacks were hanging by a thread from the board and it basically broke off in my hands. Hopefully they just need to be soldered back on. Now to find someone handy with a soldering gun...

Oh and just to clarify and give a mea culpa, I redid the out-from-preamp-output-into-aux-input-on-integrated-amp test, and realized that the signal was good that way. So no problems with the preamp output after all. Not sure how I messed up that test the first time, guess I was afraid to turn up the volume too high the first time I did it.
 

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